The invention relates to a cruise controller, which is intended for motor vehicles, and which adjusts the speed on the basis of a predefined setpoint speed.
Cruise controllers make it possible to drive at a setpoint speed, which can be adjusted by the driver, so that the driver does not have to constantly preset the speed by use of the gas pedal. These controllers are especially suitable primarily for driving on highways with little traffic congestion, since in such situations driving at a constant speed is often desired.
In addition, such cruise controllers can be equipped with an inter-vehicle distance control function. Basically, in this case the speed is adjusted on the basis of the predefined setpoint speed so long as no vehicle traveling ahead is detected. If, however, a vehicle is travelling ahead of the vehicle equipped with the cruise controller, then the speed is adjusted on the basis of a predefined desired distance, in order to maintain a safety margin in relation to this vehicle that is travelling ahead. In the event that one's own vehicle is following another vehicle (so-called “tailing”), cruise controllers that are expanded to include an inter-vehicle distance control function can adjust to the speed of the vehicle travelling ahead to some extent even up to and out of a stationary state.
In the event that the speed has been adjusted on the basis of a predefined setpoint speed, situations may occasionally arise, in which for safety reasons it would be disadvantageous to adjust the speed on the basis of the predefined speed. For this reason there already exist cruise controllers that are automatically deactivated in the event of a braking action in order to stabilize the operating dynamics.
Moreover, EP 1 726 471 A1 discloses a cruise controller with a monitoring unit for modifying the control function as a function of the condition of the roadway. To this end, the monitoring device is designed to determine and evaluate the roadway condition by way of the measured rotational speed of the wheels. If the differences between the rotational speed of the individual wheels deviate from the typical differences between the rotational speed of the wheels during cornering or owing to the drive slip, then the control function is modified, for example, in the form of switching-off the cruise controller.
Furthermore, DE 195 02 954 A1 discloses a method for controlling the vehicle speed. In this case, the current or stored roadway data about the stretch of road ahead of the vehicle can be used to preset different cruising speeds of the vehicle. Thus, a setpoint speed is determined as a function of the characteristics of the stretch of road that has been traveled and is compared with the setpoint speed that is predefined by the driver. If, for example, the determined setpoint speed, characterizing a curve, drops below the driver's predefined setpoint speed, then the correction factor for controlling the speed is calculated on the basis of the determined, lower setpoint speed.
The object of the invention is to provide a cruise controller, which considers in a simple way the current roadway data during an active cruise control.
This object is achieved by a cruise controller, which is intended for motor vehicles for the purpose of adjusting the speed on the basis of a predefined setpoint speed. The cruise controller includes a monitoring device, which evaluates vehicle state variables in order to modify the cruise control function as a function of the determined roadway data. The monitoring unit is designed to evaluate the current steering wheel angle, the current lateral acceleration, and/or the current yaw rate. Upon exceeding at least one predefined first vehicle state variable limit value by one of the evaluated vehicle state variables, the cruise control function is switched into a standby mode. Advantageous further developments are described herein.
The inventive cruise controller for adjusting the speed on the basis of a predefined setpoint speed is equipped with a monitoring device for evaluating the vehicle state variables. The monitoring unit is designed to evaluate the current steering wheel angle, the current lateral acceleration, and/or the current yaw rate. Upon exceeding at least one predefined first vehicle state variable limit value by one of the evaluated vehicle state variables, the cruise control function is switched into a standby mode. The standby mode is characterized in that although the cruise control system is switched on during this mode, it is not active. That is, the cruise control system is interrupted, and the driver is himself responsible for controlling the travelling speed.
It is possible to determine in a simple way by use of the steering wheel angle, the lateral acceleration, or the yaw rate, whether the vehicle is on a stretch of road, where it is possible under some circumstances that a speed adjustment could lead to critical situations. The said vehicle state variables are a measure for the actual geometric design feature of the lane, in particular, the radius of the curve in that stretch of road, on which the vehicle is currently travelling. If the current steering wheel angle exceeds a predefined first steering angle limit value and/or the current lateral acceleration exceeds a predefined first lateral acceleration limit value and/or the current yaw rate exceeds a predefined first yaw rate limit value, then the cruise controller is switched into a standby mode from its previously active operating mode, the active mode. As long as the driver does not specify a request to accelerate or decelerate, the vehicle is automatically decelerated on the basis of the engine brake and/or the engine drag torque. In this way, it can be guaranteed that the speed of the vehicle is automatically reduced in a simple way to a speed that is adjusted on the basis of this geometric feature of the road, as long as the driver does not do anything. For example, a value of 3 m/s2 can be preset as the first lateral acceleration limit value.
The current steering wheel angle and/or the current lateral acceleration and/or the current yaw rate can be determined through calculation either by use of a sensor, which is provided to this end, or from other signals. The vehicle state variable limit values can be preset in a fixed manner or as a variable, for example, as a function of the current speed.
In order to return from the standby mode into an active mode, in which the adjustment of the speed on the basis of a predefined setpoint speed is active again, there are a variety of alternatives. Hence, in one advantageous embodiment of the cruise controller, the monitoring device automatically switches the cruise control function back into the active mode and/or the originally active operating mode from the standby mode, if none of the evaluated vehicle state variables exceeds the predefined first vehicle state variable limit value or a predefined second vehicle state variable limit value. Thus, each of the evaluated vehicle state variables drops below its second vehicle state variable limit value. The second vehicle state variable limit values can be preset identically to the first vehicle state variable limit values. However, it is advantageous if they are preset so as to be less than the predefined first vehicle state variable limit values, so that the cruise control function is not continuously activated and deactivated. For example, a value of 2 m/s2 can be preset as the second lateral acceleration limit value.
If, therefore, neither the current steering wheel angle exceeds the predefined second steering angle limit value nor the current lateral acceleration exceeds the predefined second lateral acceleration limit value, nor the current yaw rate exceeds the predefined second yaw rate limit value, then the conclusion can be drawn that the vehicle is no longer in a sharp curve and, thus, the speed can be re-adjusted again.
In order to guarantee that the driver is not on a stretch of road that exhibits a plurality of sharp curves in succession and, thus, it would be necessary to switch multiple times from the standby mode into an active mode, one alternative embodiment of the cruise controller provides that the monitoring device does not automatically switch the cruise control function again into an active mode and/or the originally active operating mode from the standby mode until none of the evaluated vehicle state variables (steering wheel angle, lateral acceleration and/or yaw rate) exceeds one of the predefined first or second vehicle state variable limit values for a predefined time interval. Thus, each of the evaluated vehicle state variables falls below its first or second vehicle state variable limit value for a predefined time interval. In this context, the time interval can be preset in a fixed manner or as a variable as a function of the various surrounding parameters of the vehicle or as a function of the determined surrounding parameters (for example, navigation data, type of road).
As an alternative or in addition, a return from the standby mode into an active mode can also occur, if the driver actuates, for example by depressing the gas pedal or not until the actuated gas pedal is released again. Actuating the gas pedal makes it clear that the driver does not perceive or no longer perceives a decrease in speed to be necessary. As a result, the system can be returned again into an active mode.
Depending on the configuration of the controller, a return into the active mode can take place either immediately when the gas pedal is actuated or not until the actuated gas pedal has been released. An immediate return into the active mode upon actuating the gas pedal is usually not noticed by the driver, since in this case the setpoint speed always matches the current speed. As soon as the driver takes his foot from the gas pedal, he will discern the cruise control function, because the speed will be maintained, even though the gas pedal is no longer actuated.
The automatic return option, according to the first or second alternative, can be combined with the driver's consciously initiated return from the standby mode into an active mode in such a way that the actuation of the gas pedal as the return request overlaps the automatic return circuit on undershooting the corresponding vehicle state variable limit values. As soon as the driver steps on the gas pedal, it is detectable that he would like to drive faster again. If the driver releases the actuated gas pedal, the cruise control system can return into an active mode, even if at least one of the vehicle state variables, evaluated in the monitoring unit, exceeds the associated first or second vehicle state variable limit value. This is logical, because the driver should always have control over his vehicle and/or its functions.
If the system returns into the active mode owing to a gas pedal actuation (for example, due to the driver stepping on the gas pedal, or to the driver stepping on the gas pedal and subsequently releasing the gas pedal), even though at least one of the evaluated vehicle state variables exceeds one of the predefined first and/or second vehicle state variable limit values, then the conclusion is drawn that the driver perceives the predefined threshold for the vehicle state variable limit values to be too low. Therefore, when the gas pedal is released, the predefined first and/or second vehicle state variable limit value is (are) replaced. The predefined first or second vehicle state variable limit values can be replaced by the current vehicle state variables or a vehicle state variable that is increased compared to the current vehicle state variable. If the end of the curve and/or the curvilinear stretch of the road is detected with the aid of the current vehicle state variables, then the currently predefined first and second vehicle state variable limit values can be replaced again with the original vehicle state variable limit values.
If the driver does not actuate the gas pedal, the system does not switch back again into an active mode from the standby mode, until all of the evaluated vehicle state variables no longer exceed their predefined first or second vehicle state variable limit value (for a predefined time interval).
The active mode, into which the system returns, can be configured in a variety of ways. Hence, it can be equipped in a first alternative such that after switching back into the active mode—for example, either owing to the current vehicle state variables or owing to the gas pedal being actuated—the predefined setpoint speed of the vehicle at the time prior to the standby mode is preset as the setpoint speed. Then, the cruise controller would be operated again in the active operating mode that was operated prior to the standby mode at the same setpoint speed. The vehicle would be accelerated again on the basis of the original setpoint speed, and on reaching this speed, it would be maintained.
As an alternative, the active mode can also be configured such that when the system returns from the standby mode, the current speed is preset as the setpoint speed. In this way it can be guaranteed that in the event that the standby mode was active for a prolonged period of time, the driver will not become irritated due to a sudden acceleration.
As an alternative, the presetting of the setpoint speed upon returning into an active mode can also depend on the reason for switching back into the active mode. Hence, for example, in the event of a short term actuation by means of the gas pedal and, as a result, the return into the active mode, the original setpoint speed can be preset as the setpoint speed. If the driver actuates the gas pedal for a longer period of time, then the current speed at the time after the gas pedal has been released can be preset as the setpoint speed. Similarly, in the event of an automatic return into the active mode, the setpoint speed can be preset as a function of the duration of the standby mode. If the standby mode was active for just a short period of time, then the originally predefined setpoint speed can be preset as the setpoint speed. If the standby mode persists for a longer period of time, then the current speed can be preset as the setpoint speed.
As an alternative, the setpoint speed could also be preset from the difference between the current speed and the original setpoint speed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.